Generally, a specific node of a wireless communication system that uses a Frequency Division Duplex (FDD) mode outputs a transmission signal of a transmitter with strongest power when a receiver is in a weak electric field in order to control power, so that the transmission signal outputs from the transmitter is flowed to the receiver and acts as an interference signal.
Accordingly, a conventional art provides methods for removing the transmission signal flowed to the receiver. For example, a technique for removing the transmission signal by inserting an external Surface Acoustic Wave (SAW) filter into the receiver is provided. The function of the SAW filter includes a function of removing a transmission (Tx) tone and a balun function of converting a single input signal input from an antenna into a differential input signal for driving a mixer. However, a technique using the SAW filter has inconvenience of having additional external parts.
For a conventional art of a balun circuit that is realized inside an RF chip, there exists a United States patent titled “Transformer-Based Multi-Band RF Front-End Architecture” (United States Publication No. 2006/0270,377, BroadCom Inc.)
The above US Publication No. 2006/0,270,377 relates to a transformer converting a single input signal into a differential input signal, and discloses a balun circuit generating differential signals of various bands using single input from an antenna through a multiple tap of the transformer. This structure performs only a function of converting one single input signal into a plurality of differential signals, and does not perform a notch function of a Tx band which is problematic in FDD.
As described above, the conventional art removes a Tx signal flowed to the inside of a receiver by inserting a SAW filter into the outside of an RF chip, and simultaneously, performs a balun function of converting a single signal input from an antenna into a differential signal for driving a mixer, but there is inconvenience of having additional external parts.
Therefore, a receiving circuit which performs a notch function as well as a balun function realized inside an RF chip using a transformer, and an operating method thereof are required.